How to access a JavaFx Stage from a Controller?

Question

I'm converting a pure JavaFx app, in which the code below worked fine when put all in one class, to a FXML one, where the Stage declaration and the button handler are in separate classes. In the a Controller, I'm trying to implement a method that will allow the user to choose a directory and store it in a variable for later use:

private File sourceFile;
DirectoryChooser sourceDirectoryChooser;

@FXML
private void handleSourceBrowse() {
        sourceDirectoryChooser.setTitle("Choose the source folder");
        sourceFile = sourceDirectoryChooser.showDialog(theStage);
}

However, "theStage", a Stage which the method requires, only exists(if that's the right terminology) in FolderSyncer4.java:

public class FolderSyncer4 extends Application {

    final String FOLDER_SYNCER = "FolderSyncer";

    Stage theStage;

    @Override
    public void start(Stage primaryStage) throws Exception {
        theStage = primaryStage;

        //TODO do the FXML stuff, hope this works
        Parent root = FXMLLoader.load(getClass().getResource("FolderSyncerMainWindow.fxml"));
        theStage.setScene(new Scene(root, 685, 550));
        theStage.setTitle(FOLDER_SYNCER);
        theStage.show();
    }
}

How to I get around this? I need to have that method implemented again somehow, but suddenly I can't pass the stage as an argument.

Solution 1

In your situation, it is probably easiest to get the scene from the ActionEvent parameter of your handler:

@FXML
private void handleSourceBrowse(ActionEvent ae) {
    Node source = (Node) ae.getSource();
    Window theStage = source.getScene().getWindow();

    sourceDirectoryChooser.showDialog(theStage);
}

See JavaFX: How to get stage from controller during initialization? for some more information. I am not in favor of the highest rated answer though, since it adds a compile time dependency to the controller after the .fxml file has been loaded (after all that question was tagged with javafx-2, so not sure if the above approach already worked there, and also the context of the question looks a bit different).

See also How do I open the JavaFX FileChooser from a controller class?

Solution 2

Another way is define a static getter for the Stage and Access it

Main Class

public class Main extends Application {
    private static Stage primaryStage; // **Declare static Stage**

    private void setPrimaryStage(Stage stage) {
        Main.primaryStage = stage;
    }

    static public Stage getPrimaryStage() {
        return Main.primaryStage;
    }

    @Override
    public void start(Stage primaryStage) throws Exception{
        setPrimaryStage(primaryStage); // **Set the Stage**
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root, 300, 275));
        primaryStage.show();
    }
}

Now you Can access this stage by calling

Main.getPrimaryStage()

In Controller Class

public class Controller {
public void onMouseClickAction(ActionEvent e) {
    Stage s = Main.getPrimaryStage();
    s.close();
}
}

Comments

[Sargon1]

I thank you for your answer, but this implementation gives a java.lang.reflect.InvocationTargetException when the button is pressed.

[Andreas Fester]

Thats strange - I tested it with a simple example, see github.com/afester/CodeSamples/tree/master/Java/JavaFXSample‌​/…. Can you paste the stack trace from the exception to pastebin.com or something similar and add the link to it as a comment?

[Sargon1]

Here it is. Thanks for the help, I'm not too good at deciphering those things. pastebin.com/3AycwLge

[Andreas Fester]

Ok, so the root cause is a NullPointerException in line 75 of your controller class - what is the contents of that line?

[Andreas Fester]

So, according to your code in the question, did you probably forget to create the DirectoryChooser, like DirectoryChooser sourceDirectoryChooser = new DirectoryChooser();? That would also explain the NPE.

[Sargon1]

Yup, just figured it out too. It seem s to be working now, thanks.

[Koin Arab]

Very nice solution but the getter and setter should be static here.